A superconducting wire is manufactured by superposing a metal substrate, an intermediate layer composed of one or more layers of oxides, such as cerium oxide (CeO2), yttria-stabilized zirconia (YSZ), and yttrium oxide (Y2O3), and a superconducting layer (RE123 film, RE: Y, Gd, Ho, or the like) on top of each other.
Methods known as techniques for manufacturing crystal-oriented superconducting layers are: the ion-beam-assisted deposition method (IBAD method) that involves depositing a textured intermediate layer on a non-textured metal substrate such as hastelloy, so as to allow the superconducting layer to take on the texture; and a method that involves the use of a biaxially textured metal substrate, so as to allow the intermediate layer and the superconducting layer to take on the texture (e.g., a method involving the use of a rolling-assisted biaxially textured substrate (RABiTS)). The latter method is more advantageous than the former in view of factors concerning future production efficiency, such as film deposition rate. In order to improve superconductivity, a metal substrate is required to have a high degree of biaxial crystal orientation. The crystal orientation of a metal substrate is evaluated in terms of, for example, the c-axis orientation rate or the Δφ value of the outermost layer of the substrate.
A substrate known as such a metal substrate (a substrate for a superconducting wire) is produced by superposing crystal-oriented copper on a stainless substrate and further superposing nickel thereon. For example, Patent Document 1 discloses a clad textured metal substrate for forming an epitaxial thin film comprising a metal layer and a copper layer bonded to at least one surface of the metal layer. The copper layer has a {100} <001> cube texture, provided that a Δφ is 6 degrees or less (Δφ≤6°).
Furthermore, Patent Document 2 discloses a method for manufacturing a metal substrate for a superconducting wire, which comprises laminating a non-magnetic metal plate and a metallic foil made of Cu or a Cu alloy, which has been cold-rolled at high reduction, through surface activation bonding, biaxially crystal-orienting the metallic foil by thermal treatment after lamination, and thus providing an Ni or Ni alloy epitaxial growth film on the surface of the metallic foil. Patent Document 2 describes that the metal substrate obtained by such method achieved an improved crystal orientation rate and a Δφ of the Ni-plated layer of the outermost layer.
Patent Document 3 discloses a method of manufacturing a metal substrate for a superconducting wire comprising steps of removing a material adsorbed onto a surface of the copper foil by applying sputter etching to the surface of the copper foil, removing a material adsorbed onto a surface of a non-magnetic metal plate by applying sputter etching to the surface of the non-magnetic metal plate, bonding the copper foil and the metal plate to each other using pressure rolls at an applied pressure of 300 MPa to 1500 MPa, heating the bonded laminate to a crystal orientation temperature of copper or above, so as to orient crystals of the copper, and forming a protective layer on a copper-side surface of the laminate by coating. Patent Document 3 describes that the metal substrate obtained by such method achieved an improved c-axis crystal orientation rate and a Δφ of the copper foil and of the Ni-plated layer.